Group 13 element nitride layer, free-standing substrate and functional element

ABSTRACT

It is provided a layer of a crystal of a nitride of a group 13 element selected from gallium nitride, aluminum nitride, indium nitride and the mixed crystals thereof, and the layer includes an upper surface and a bottom surface. The upper surface includes a linear high-luminance light-emitting part and a low-luminance light-emitting region adjacent to the high-luminance light-emitting part, and the high-luminance light-emitting part has a portion extending along an m-plane of the crystal of the nitride of the group 13 element, in the case that the upper surface is observed by cathode luminescence. The upper surface has an arithmetic average roughness Ra of 0.05 nm or more and 1.0 nm or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of PCT/JP2018/028558,filed Jul. 31, 2018, corresponding to PCT/JP2017/030373, filed Aug. 24,2017, PCT/JP2017/034035, filed Sep. 21, 2017 and Japanese ApplicationNo. 2018-061553, filed Mar. 28, 2018, the entire contents all of whichare incorporated hereby by reference.

TECHNICAL FIELD

The present invention relates to a layer of a nitride of a group 13element, a free-standing substrate and a functional device.

BACKGROUND ARTS

It has been known light emitting devices such as light emitting diodes(LEDs) that use sapphire (α-alumina single crystal) as a monocrystallinesubstrate, with various types of gallium nitride (GaN) layers formedthereon. For example, light emitting devices have been mass-producedhaving a structure in which an n-type GaN layer, a multiple quantum well(MQW) layer with an InGaN quantum well layer and a GaN barrier layerlaminated alternately therein and a p-type GaN layer are formed in alaminated manner in this order on a sapphire substrate.

Patent document 1 describes a gallium nitride layer composed ofpolycrystalline gallium nitride having many gallium nitridemonocrystalline grains, including many columnar gallium nitridemonocrystalline grains laterally arranged.

Patent document 2 describes a gallium nitride layer composed ofpolycrystalline gallium nitride having many gallium nitridemonocrystalline grains, including many columnar gallium nitridemonocrystalline grains laterally arranged. Further, an average tiltangle on a surface (an average value of inclination of crystalorientation (crystalline axis) with respect to a normal line of thesurface) is 1° to 10°.

According to patent document 3, inclusions are contained at a highconcentration from a bottom surface to an intermediate position, andbetween the intermediate position and the upper surface, a plurality ofgrain boundaries having a low concentration of the inclusions are formedfrom the bottom surface in a diagonal direction. Further, the grainboundaries are elongated in the diagonal direction of an angle of 50 to70° with respect to c-axis.

Patent document 5 describes gallium nitride crystal having a lowdislocation density by increasing a ratio of Ga in a melt.

RELATED ART DOCUMENTS Patent Documents

(Patent document 1) Japanese Patent No. 5770905B(Patent document 2) Japanese Patent No. 6154066B(Patent document 3) Japanese Patent No. 5897790B(Patent document 4) WO 2011/046203 A1(Patent document 5) WO 2010/084682 A1

SUMMARY OF THE INVENTION Object to be Solved by the Invention

In the case that a light-emitting device is produced on the galliumnitride crystal of patent document 1 or 2, it is proved that currentpath may be interrupted resulting in a reduction of luminanceefficiency, although it is dependent on balance between a size of thedevice and grain size. Although the reasons are not clear, anisotropicproperty of the orientations of the monocrystalline grains may affectthe reduction.

According to gallium nitride crystals of patent documents 3 and 4, asits size is made larger, it may be difficult to control the flow of themelt over the whole surface of a substrate so that voids may be left onthe peripheral part of the crystal.

According to patent document 5, although it is possible to reduce thedislocation density by applying a high Ga ratio and by controlling theflow of the flux to increase the grain size, voids tend to be includedbetween the grains.

An object of the present invention is, in a layer of a crystal of agroup 13 nitride having an upper surface and lower surface and composedof a crystal of the group 13 nitride selected from gallium nitride,aluminum nitride, indium nitride or the mixed crystals thereof, toprovide microstructure capable of reducing a dislocation density andreducing the deviation of a property as a whole.

The present invention provides a layer of a crystal of a nitride of agroup 13 element, said crystal of said nitride being selected fromgallium nitride, aluminum nitride, indium nitride and the mixed crystalsthereof and said layer comprising an upper surface and a bottom surface:

wherein said upper surface comprises a linear high-luminancelight-emitting part and a low-luminance light-emitting region adjacentto said high-luminance light-emitting part and said high-luminancelight-emitting part comprises a portion extending along an m-plane ofsaid crystal of said nitride of said group 13 element, said uppersurface being observed by cathode luminescence; and

wherein said upper surface has an arithmetic average roughness Ra of0.05 nm or more and 1.0 nm or less.

The present invention further provides a free-standing substratecomprising the layer of the crystal of the nitride of the group 13element.

The present invention further provides a composite substrate comprising:

a supporting body; and

the layer of the nitride of the group 13 element provided on thesupporting body.

The present invention further provides a functional device comprising:

the free-standing substrate; and

a functional layer provided on the layer of the crystal of the nitrideof the group 13 element.

The present invention further provides a functional device comprising:

the composite substrate; and

a functional layer provided on the layer of the crystal of the nitrideof the group 13 element.

According to the present invention, in the case that the upper surfaceof the layer of the crystal of the nitride of the group 13 element isobserved by cathode luminescence, the layer includes the linearhigh-luminance light-emitting part and the low-luminance light-emittingregion adjacent to the high-luminance light-emitting part, and thehigh-luminance light-emitting part includes a portion extending alongm-plane of the crystal of the group 13 nitride. The linearhigh-luminance light-emitting part appears on the upper surface,indicating that dopant and minute components and the like contained inthe crystal of the group 13 nitride form the thick high-luminancelight-emitting part. At the same time, the linear high-luminancelight-emitting part extends along the m-plane, indicating that dopantsare concentrated along the m-plane during the crystal growth and thatthe thick linear high-luminance light-emitting part thereby appearsalong the m-plane.

According to the layer of the crystal of the group 13 nitride having thenovel microstructure, it is possible to provide the layer of the crystalof the group 13 nitride in which the dislocation density can be madelower and the deviation of a property can be reduced as a whole, even inthe case of a larger size (for example, the diameter is made 6 inches orlarger).

In addition to this, the arithmetic average roughness Ra on the uppersurface of the layer of the crystal of the group 13 nitride is 0.05 nmor more and 1.0 nm or less. It is thus possible to suppress thegeneration of surface pits in epitaxially growing a functional devicelayer, such as an LD device or LED device, on the upper surface of thelayer of the crystal of the group 13 nitride.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) shows the state that an alumina layer 2, a seed crystal layer3 and a layer 13 of a crystal of a group 13 nitride are provided on asupporting body 1, and FIG. 1(b) shows the layer 13 of the crystal ofthe group 13 nitride separated from the supporting body.

FIG. 2 is a diagram schematically illustrating a cathode luminescenceimage of an upper surface 13 a of the layer 13 of the crystal of thegroup 13 nitride.

FIG. 3 is a photograph showing a cathode luminescence image of an uppersurface 13 a of the layer 13 of the crystal of the group 13 nitride.

FIG. 4 is a photograph showing an enlarged view of FIG. 3.

FIG. 5 is a diagram corresponding with the cathode luminescence image ofFIG. 4.

FIG. 6 is a photograph showing a cathode luminescence image of a crosssection of the layer 13 of the crystal of the group 13 nitride.

FIG. 7 is a photograph taken by a scanning type electron microscopeshowing a cross section of the layer 13 of the crystal of the group 13nitride.

FIG. 8 is a diagram schematically showing a functional device 21 of thepresent invention.

FIG. 9 is a photograph taken by a scanning type electron microscope ofan upper surface of the layer of the crystal of the group 13 nitride.

FIG. 10 shows a histogram of a gray scale generated from the CL image.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The present invention will be described further in detail.

(Layer of Crystal of Group 13 Nitride)

A layer of a crystal of a group 13 nitride of the present invention iscomposed of a crystal of a group 13 nitride selected from galliumnitride, aluminum nitride, indium nitride and the mixed crystalsthereof, and includes an upper surface and bottom surface. For example,as shown in FIG. 1(b), the upper surface 13 a and bottom surface 13 b ofthe layer 13 of the crystal of the group 13 nitride are opposed witheach other.

The nitride forming the layer of the crystal of the group 13 nitrideincludes gallium nitride, aluminum nitride, indium nitride or the mixedcrystal thereof. It is specifically listed GaN, AlN, InN,Ga_(x)Al_(1-x)N (1>x>0), Ga_(x) In_(1-x)N (1>x>0) andGa_(x)Al_(y)In_(z)N (1>x>0, 1>y>0, x+y+z=1).

More preferably, the nitride forming the layer of the crystal of thegroup 13 nitride is a gallium nitride series nitride. It is specificallylisted GaN, Ga_(x)Al_(1-x)N (1>x>0.5), Ga_(x)In_(1-x)N (1>x>0.4) andGa_(x)Al_(y)In_(z)N (1>x>0.5, 1>y>0.3, x+y+z=1).

The nitride of the group 13 element may be doped with zinc, calcium orthe other n-type dopant or p-type dopant, and in this case, thepolycrystalline group 13 nitride can be used as a member or a layerother than the base material, such as a p-type electrode, an n-typeelectrode, a p-type layer, or an n-type layer. A preferable example ofp-type dopants may be one type or more selected from the groupconsisting of beryllium (Be), magnesium (Mg), strontium (Sr), andcadmium (Cd). A preferable example of n-type dopant may be one type ormore selected from the group consisting of silicon (Si), germanium (Ge),tin (Sn), and oxygen (O).

Here, in the case that the upper surface 13 a of the layer 13 of thecrystal of the group 13 nitride is observed by cathode luminescence(CL), as schematically shown in FIG. 2, the upper surface 13 a includesthe linear high-luminance light-emitting part 5 and low-luminancelight-emitting region 6 adjacent to the high-luminance light-emittingpart 5.

Here, the observation by CL is performed as follows. It is used ascanning type electron microscope (SEM) with a CL detector for the CLobservation. For example, in the case that it is used a scanning typeelectron microscope (“S-3400N” supplied by HITACHI Hi Technologies Co.Ltd.) equipped with Mini CL system produced by Gatan, it is preferred toinsert the Cl detector between a sample and an object lens under themeasurement conditions of an acceleration voltage of 10 kV, probecurrent “90”, at a working distance (W. D.) of 22.5 mm and a magnitudeof 50 folds.

Further, the high-luminance light-emitting part and low-luminancelight-emitting region are distinguished based on the observation by thecathode luminescence as follows.

As to brightness of an image observed by CL under the conditions of anacceleration voltage of 10 kV, probe current “90”, at a working distance(W. D.) of 22.5 mm and a magnitude of 50 folds, it is used an imageprocessing software (for example, “WinRoof Ver 6.1.3” supplied by Mitanicorporation) to prepare a histogram of gray scale of 256 grades whosevertical axis shows a degree and horizontal axis shows brightness(GRAY). As shown in FIG. 10, two peaks are confirmed in the histogram.The brightness at which the degree takes its minimum value between thetwo peaks is defined as a boundary, and the higher side is defined asthe high-luminance light emitting part and the lower side is defined asthe low-luminance light-emitting region.

Further, on the upper surface of the layer of the crystal of the group13 nitride, the linear high-luminance light emitting part andlow-luminance light-emitting region are adjacent to each other. Theadjacent low-luminance light-emitting regions are distinguished by thelinear high-luminance light-emitting part between them. Here, thelinearity of the high-luminance light-emitting part means that thehigh-luminance light-emitting part is elongated lengthwise between theadjacent low-luminance light-emitting regions to provide a boundaryline.

Here, the line of the high-luminance light emitting part may be astraight line, curved line or a combination of the straight line andcurved line. The curved line includes various shapes such as circle,ellipse, parabola and hyperbola. Further, the high-luminance lightemitting parts extending in different directions may be continuous witheach other, and an end of the high-luminance light-emitting part may bediscontinued.

On the upper surface of the layer of the crystal of the group 13nitride, the low-luminance light-emitting region may be the exposedsurface of the crystal of the group 13 nitride grown thereunder and isextended two-dimensionally and in a planar shape. On the other hand, thehigh-luminance light-emitting part is of a linear shape and extendedone-dimensionally to provide the boundary line dividing the adjacentlow-luminance light-emitting regions. For example it is considered thatdopant components, minute components and the like are discharged fromthe crystal of the group 13 nitride grown from the bottom andconcentrated between the nitride crystals adjacent with each otherduring the growth, thereby generating linear and strong light-emittingpart between the adjacent low-luminance light-emitting regions on theupper surface.

For example, FIG. 3 shows a photograph taken by CL observation of theupper surface of the layer of the crystal of the group 13 nitrideobtained in the inventive example. FIG. 4 is an enlarged view of FIG. 3,and FIG. 5 schematically shows a diagram corresponding to FIG. 4. It isproved that the low-luminance light-emitting region is extendedtwo-dimensionally, and the high-luminance light-emitting part islinear-shaped and elongated one-dimensionally as the boundary linedividing the adjacent low-luminance light-emitting regions.

As such, the shape of the low-luminance light-emitting region is notparticularly limited, and normally elongated planarly andtwo-dimensionally. On the other hand, it is necessary that the line ofthe high-luminance light-emitting part is of an elongate shape. On theviewpoint, the width of the high-luminance light-emitting part maypreferably be 100 μm or smaller, more preferably be 20 μm or smaller andparticularly preferably be 5 μm or smaller. Further, the width of thehigh-luminance light-emitting part is normally 0.01 μm or larger.

Further, on the viewpoint of the present invention, the ratio(length/width) of the length and width of the high-luminancelight-emitting part may preferably be 1 or more and more preferably be10 or more.

Further, on the viewpoint of the present invention, on the uppersurface, the ratio of the area of the high-luminance light-emittingparts with respect to the area of the low-luminance light-emittingregions (area of high-luminance light-emitting parts/area oflow-luminance light-emitting regions) may preferably be 0.001 or moreand more preferably be 0.01 or more.

Further, on the viewpoint of the present invention, on the uppersurface, the ratio of the area of the high-luminance light-emittingparts with respect to the area of the low-luminance light-emittingregions (area of high-luminance light-emitting parts/area oflow-luminance light-emitting regions) may preferably be 0.3 or less andmore preferably be 0.1 or less.

According to a preferred embodiment, the high-luminance light-emittingpart includes a portion extending along the m-plane of the crystal ofthe nitride of the group 13 element. For example, according to theexamples shown in FIGS. 2 and 5, the high-luminance light-emitting part5 is elongated in an elongate shape and includes portions 5 a, 5 b and 5c elongating along the m-plane. The directions along the m-plane of thehexagonal crystal of the nitride of the group 13 element is,specifically, [−2110], [−12-10], [11-20], [2-1-10], [1-210] or [−1-120]direction. The high-luminance light-emitting part 5 includes a part of aside of a substantially hexagonal shape reflecting the hexagonalcrystal. Further, the linear high-luminance light-emitting part iselongated along the m-plane, meaning that the lengthwise direction ofthe high-luminance light-emitting part is elongated in the direction ofeach of [−2110], [−12-10], [11-20], [2-1-10], [1-210] and [−1-120].Specifically, it is permitted that the lengthwise direction of thelinear high-luminance light-emitting part is inclined preferably by ±1°and more preferably by ±0.3° with respect to the m-plane.

According to a preferred embodiment, on the upper surface, the linearhigh-luminance light-emitting part is elongated approximately along them-plane of the crystal of the nitride of the group 13 element. It meansthat a main portion of the high-luminance light-emitting part iselongated along the m-plane and preferably the continuous phase of thehigh-luminance light-emitting part is elongated approximately along them-plane. In this case, the portion extending in the direction along them-plane may preferably occupy 60 percent or more, more preferably 80percent or more and may occupy substantially the whole of the wholelength of the high-luminance light-emitting part.

Further, according to the present invention, the arithmetic averageroughness Ra of the upper surface of the layer of the crystal of thegroup 13 nitride is 0.05 nm or more and 1.0 nm or less.

The arithmetic average roughness Ra is an average value of absolutedeviation values from an average line and measured according to “JIS0601”.

According to a preferred embodiment, on the upper surface of the layerof the crystal of the group 13 nitride, the high-luminancelight-emitting part constitute continuous phase and the low-luminancelight-emitting region constitutes discontinuous phases divided by thehigh-luminance light-emitting part. For example, as shown in theschematic views of FIGS. 2 and 5, the linear high-luminancelight-emitting part 5 forms the continuous phase and the low-luminancelight-emitting regions 6 forms the discontinuous phases divided by thehigh-luminance light-emitting part 5.

Here, although the continuous phase means that the high-luminancelight-emitting part 5 is continuous on the upper surface, it does notnecessarily mean that all the high-luminance light emitting parts 5 arecompletely continuous, and it is permitted that a small part of thehigh-luminance light-emitting part 5 is separated from the otherhigh-luminance light-emitting part 5 as far as it does not affect thewhole pattern.

Further, the dispersed phase means that the low-luminance light-emittingregions 6 are approximately divided by the high-luminance light-emittingpart 5 into many regions which are not continuous. Further, in the casethat the low-luminance light-emitting regions 6 are divided by thehigh-luminance light-emitting part 5 on the upper surface, it ispermitted that the low-luminance light-emitting regions 6 are continuousinside of the layer of the crystal of the group 13 nitride.

According to a preferred embodiment, the half value width of thereflection at (0002) plane of X-ray rocking curve on the upper surfaceof the crystal layer of the group 13 nitride is 3000 seconds or less and20 seconds or more. It indicates that the surface tilt angle is low andthe crystal orientations are highly oriented, as a whole, as a singlecrystal, on the upper surface. As the microstructure has the cathodeluminescence distribution as described above and the crystalorientations at the surface are highly orientated as a whole as such, itis possible to reduce the distribution of property on the upper surfaceof the layer of the crystal of the group 13 nitride, to obtain uniformproperties of various kinds of functional devices provided thereon andto improve the yield of the functional devices.

On the viewpoint, the half value width of the reflection at (0002) planeof X-ray rocking curve on the upper surface of the crystal layer of thegroup 13 nitride may preferably be 1000 seconds or less and 20 second ormore, and more preferably be 500 seconds or less and 20 seconds or more.Here, it is actually difficult to make the half value width of thereflection at (0002) plane of X-ray rocking curve on the upper surfaceof the crystal layer of the group 13 nitride lower than 20 seconds.

Further, the reflection at (0002) plane of the rocking curve is measuredas follows. It is used an XRD system (for example, D8-DISCOVER suppliedby Bruker-AXS) to perform the measurement under conditions of a tubevoltage of 40 kV, a tube current of 40 mA, a collimator size of 0.1 mm,an anti-scattering slit of 3 mm, a range of ω=angle of peak position of±0.3°, an ω step width of 0.003° and a counting time of 1 second.According to the measurement, it is preferred to use a Ge (022)non-symmetrical monochromator to convert CuKα ray to parallel andmonochrome ray (half value width of 28 seconds) and to perform themeasurement after standing the axis at a tilt angle CHI of about 0°.Then, the half value width of reflection at (0002) plane of X-rayrocking curve can be calculated by using an XRD analysis software(supplied by Bruker-AXS, LEPTOS4.03) and performing peak search. It ispreferred to apply peak search condition of Noise filter “10”, Threshold“0.30” and Points “10”.

In the case that it is observed a cross section substantiallyperpendicular to the upper surface of the crystal layer of the group 13nitride is observed by CL, as shown in FIG. 6, it may be observed linearhigh-luminance light-emitting parts emitting white light. Here, as shownin FIG. 6, it is proved that the low-luminance light-emitting region isextended planarly and two-dimensionally and that the high-luminancelight-emitting part is elongated linearly to form a kind of a boundaryline dividing the adjacent low-luminance light-emitting regions. Themethod of observing such high-luminance light-emitting part andlow-luminance light emitting region is same as the method of observingthe high-luminance light-emitting part and low-luminance light emittingregion on the upper surface.

The shape of the low-luminance light emitting region on the crosssection of the layer of the crystal of the group 13 nitride is notparticularly limited, and is normally elongated planarly andtwo-dimensionally. On the other hand, it is necessary that the lineformed by the high-luminance light-emitting part is of an elongateshape. On the viewpoint, the width of the high-luminance light-emittingpart may preferably be 100 μm or smaller and more preferably be 20 μm orsmaller. Further, the width of the high-luminance light-emitting part isnormally 0.01 μm or larger.

Further, on the viewpoint of the present invention, the ratio of thelength and width (length/width) of the light-emitting part at the crosssection of the crystal layer of the group 13 nitride may preferably be 1or larger and more preferably be 10 or larger.

According to a preferred embodiment, on the cross section substantiallyperpendicular to the upper surface of the layer of the crystal of thegroup 13 nitride, the linear high-luminance light-emitting part forms acontinuous phase, and the low-luminance light-emitting region formsdiscontinuous phase divided by the high-luminance light-emitting part.For example, according to a photograph taken by CL of FIG. 6, the linearhigh-luminance light-emitting part forms the continuous phase, and thelow-luminance light-emitting region forms the discontinuous phasedivided by the high-luminance light-emitting part.

Here, the continuous phase means that the high-luminance light-emittingpart is continuous on the cross section and does not necessarily meanthat all the high-luminance light-emitting parts are completelycontinuous. It is thus approved that a small portion of thehigh-luminance light-emitting parts are separated from the otherhigh-luminance light emitting parts as far as it does not affect thewhole pattern.

Further, the discontinuous phase means that the low-luminancelight-emitting regions are approximately divided by the high-luminancelight emitting part into many regions which are not continuous.

According to a preferred embodiment, voids are not observed on the crosssection substantially perpendicular to the upper surface of the layer ofthe crystal of the group 13 nitride. That is, as shown in the SEMphotograph of FIG. 7 in the same visual field as the CL photograph ofFIG. 6, voids (spaces) and crystal phases other than the crystal of thegroup 13 nitride are not observed. Here, the presence of the voids isobserved as follows.

The voids are observable by observing the cross section substantiallyperpendicular to the upper surface of the layer of the crystal of thegroup 13 nitride by a scanning type electron microscope (SEM), and thevoid is defined as a space whose maximum width is 1 μm to 500 μm. It isused a scanning type electron microscope (“5-3400N” supplied by HITACHIHi Technologies Co. Ltd.) for the SEM observation, for example. It ispreferred to apply the measurement conditions of an acceleration voltageof 15 kV, a probe current “60”, a working distance (W. D.) of 6.5 mm anda magnitude of 100 folds.

Further, in the case that the cross section substantially perpendicularto the upper surface of the layer of the crystal of the group 13 nitrideis observed by the scanning type electron microscope (under themeasurement conditions as described above), it is not observed cleargrain boundaries accompanied with structural macro defects such asvoids. According to such microstructure, it is considered that theincrease of resistance or deviation of a property due to the clear grainboundaries can be suppressed in the case that a functional device suchas a light-emitting device is produced on the layer of the crystal ofthe group 13 nitride.

Further, according to a preferred embodiment, the dislocation density onthe upper surface of the layer of the crystal of the group 13 nitride is1×10²/cm² or more and 1×10⁶/cm² or less. It is particularly preferred tomake the dislocation density 1×10⁶/cm² or less, on the viewpoint ofimproving the properties of the functional device. On the viewpoint, thedislocation density is more preferably 1×10⁴/cm² or less. Thedislocation density is to be measured as follows.

It may be used a scanning type electron microscope (SEM) with a CLdetector for the measurement of the dislocation density. For example, inthe case that it is used a scanning type electron microscope (“S-3400N”supplied by HITACHI Hi Technologies Co. Ltd.) equipped with Mini CLsystem produced by Gatan for the CL observation, the dislocatedpositions are observed as dark spots without emitting light. The densityof the dark spots is measured to calculate the dislocation density. Itis preferably measured under the measurement conditions of anacceleration voltage of 10 kV, a probe current “90”, a working distance(W. D.) of 22.5 mm and a magnitude of 1200 folds, while the CL detectoris inserted between a sample and an object lens.

Further, according to a preferred embodiment, the half value widths ofthe reflection at the (0002) plane and of the reflection at the (1000)plane of the X-ray rocking curve on the upper surface of the crystallayer of the group 13 nitride are 3000 seconds or less and 20 seconds ormore and 10000 seconds or less and 20 seconds or more, respectively. Itmeans that both of the surface tilt angle and surface twist angle on theupper surface are low, and that the crystal orientations are highlyorientated as a whole as s single crystal. As the microstructure has thecrystal orientations at the surface highly orientated as a whole assuch, it is possible to reduce the distribution of property on the uppersurface of the layer of the crystal of the group 13 nitride, to obtainuniform properties of various functional devices provided thereon and toimprove the yield of the functional devices.

Further, according to a preferred embodiment, the half value width ofthe reflection at (1000) plane of the X-ray rocking curve on the uppersurface of the crystal layer of the group 13 nitride is 10000 seconds orless and 20 seconds or more. It indicates that the surface twist angleis very low on the upper surface and that the crystal orientations arehighly orientated as a whole as a single crystal. As the microstructurehas the cathode luminescence distribution as described above and thecrystal orientations on the surface are highly orientated as a whole assuch, it is possible to reduce the distribution of property at the uppersurface of the crystal layer of the group 13 nitride, to obtain uniformproperties of various functional devices provided thereon and to improvethe yield of the functional devices.

On the viewpoint, the half value width of the reflection at (1000) planeof the X-ray rocking curve on the upper surface of the crystal layer ofthe group 13 nitride may preferably be 5000 seconds or less, morepreferably be 1000 seconds or less and more preferably be 20 seconds ormore. Further, it is actually difficult to make the half value width toa value lower than 20 seconds.

Further, the reflection at (1000) plane of the X-ray rocking curve ismeasured as follows. It is used an XRD system (for example, D8-DISCOVERsupplied by Bruker-AXS) to perform the measurement under conditions of atube voltage of 40 kV, a tube current of 40 mA, no collimator, ananti-scattering slit of 3 mm, a range of ω=angle of peak position of±0.3°, an co step width of 0.003° and a counting time of 4 seconds.According to the measurement, it is preferred to use a Ge (022)non-symmetrical reflection monochromator to convert CuKα ray to paralleland monochrome ray (half value width of 28 seconds) and to perform themeasurement after standing the axis at a tilt angle CHI of about 88°.Then, the half value width of reflection at (1000) plane of X-rayrocking curve can be calculated by using an XRD analysis software(supplied by Bruker-AXS, LEPTOS4.03) and performing peak search. It ispreferred to apply peak search condition of Noise Filter “10”, Threshold“0.30” and Points “10”.

(Preferred Example of Production)

It will be exemplified a preferred embodiment of production of thecrystal layer of the group 13 nitride.

The crystal layer of the group 13 nitride can be produced by forming aseed crystal layer on an underlying substrate and by forming the layerof the crystal of the group 13 nitride.

For example, as exemplified in FIG. 1, it is used the underlyingsubstrate formed by forming an alumina layer 2 on a single crystalsubstrate 1. The material of the single crystal substrate 1 includessapphire, AlN template, GaN template, free-standing GaN substrate, SiCsingle crystal, MgO single crystal, spinel (MgAl₂O₄), LiAlO₂, LiGaO₂,and perovskite composite oxide such as LaAlO₃, LaGaO₃ or NdGaO₃ and SCAM(ScAlMgO₄). Further, it may be used a cubic perovskite composite oxiderepresented by the composition formula [A_(1-y)(Sr_(1-x)Ba_(x))_(y)][(Al_(1-z)Ga_(z))_(1-u)D_(u)]O₃ (wherein A is a rare earth element; D isone or more element selected from the group consisting of niobium andtantalum; y=0.3 to 0.98; x=0 to 1; z=0 to 1; u=0.15 to 0.49; and x+z=0.1to 2).

The method of forming the alumina layer 2 includes known methods such assputtering, MBE (molecular beam epitaxy), vapor deposition, mist CVDmethod, sol-gel method, aerosol deposition (AD) method, and the methodof producing an alumina sheet by tape casting or the like and adheringthe alumina sheet onto the single crystal substrate, and sputtering isparticularly preferred. Optionally, the alumina layer may be subjectedto heat treatment, plasma treatment or ion beam irradiation after theformation. The method of heat treatment is not particularly limited, andthe heat treatment may be performed under air atmosphere, vacuum,reducing atmosphere such as hydrogen or the like or inert atmospheresuch as nitrogen, argon or the like. The heat treatment may be furtherperformed under a pressure using a hot press (HP) furnace, a hotisostatic press (HIP) furnace or the like.

It may be further used, as the underlying substrate, a sapphiresubstrate subjected to the heat treatment, plasma treatment or ion beamirradiation as described above.

Then, as shown in FIG. 1(a), a seed crystal layer 3 is provided on thealumina layer 2 produced as described above or on the single crystalsubstrate subjected to the heat treatment, plasma treatment or ion beamirradiation as described above. The material forming the seed crystallayer 3 is composed of one or two or more kind of nitride of a group 13element defined by IUPAC. The group 13 element is preferably gallium,aluminum, or indium. Specifically, the crystal of the nitride of thegroup 13 element may preferably be GaN, AlN, InN, Ga_(x)Al_(1-x)N(1>x>0), Ga_(x)In_(1-x)N (1>x>0) or Ga_(x)Al_(y)InN (1>x>0, 1>y>.

Although the method of forming the seed crystal layer 3 is notparticularly limited, it may be preferably listed vapor phase processessuch as MOCVD (metal organic chemical vapor deposition), MBE (molecularbeam epitaxy), HVPE (hydride vapor epitaxy), sputtering and the like,liquid phase processes such as Na flux method, ammonothermal method,hydrothermal method and sol-gel method, a powder method utilizing solidphase growth of powder, and the combinations thereof.

For example, in the case that the seed crystal layer is formed by MOCVDmethod, preferably, a low-temperature GaN buffer layer is deposited in20 to 50 nm at 450 to 550° C. and a GaN film is then deposited in athickness of 2 to 4 μm at 1000 to 1200° C.

The crystal layer 13 of the group 13 nitride is formed so that thecrystal orientations approximately conform to the crystal orientationsof the seed crystal layer 3. The method of forming the crystal layer 13of the group 13 nitride is not particularly limited as long as itscrystalline orientation is substantially aligned with the crystalorientation of the seed crystal film and/or seed crystal layer. It maybe preferably listed vapor phase methods such as MOCVD, HVPE and thelike, liquid phase methods such as Na flux method, ammonothermal method,hydrothermal method and sol-gel method, a powder method utilizing solidphase growth of powder, and the combinations thereof. It is particularlypreferred to be performed by Na flux method.

In the case that the crystal layer of the group 13 nitride is formed byNa flux method, it is preferred to strongly agitate melt and to mix themelt uniformly and sufficiently. Although such agitation method includesswinging, rotation and vibration, the method is not limited.

The formation of the crystal layer of the group 13 nitride by Na fluxmethod may preferably be performed by filling, in a crucible with theseed crystal substrate provided therein, melt composition containing agroup 13 metal, Na metal and optionally a dopant (for example, an n-typedopant such as germanium (Ge), silicon (Si), oxygen or the like or ap-type dopant such as beryllium (Be), magnesium (Mg), calcium (Ca),strontium (Sr), zinc (Zn), cadmium (Cd) or the like, by elevating thetemperature and pressure to 830 to 910° C. and 3.5 to 4.5 MPa undernitrogen atmosphere, and then by rotating the crucible while thetemperature and pressure are held. The holding time may be made 10 to100 hours, although it is different depending on the target filmthickness.

Further, the thus obtained gallium nitride crystal produced by Na fluxmethod may preferably be subjected to grinding by a grinder to make thesurface flat, and the surface may preferably be flattened by lappingusing diamond grinding stones.

(Method of Separating Layer of Crystal of Group 13 Nitride)

Then, the layer of the crystal of the group 13 nitride may be separatedfrom the single crystal substrate to obtain a free-standing substrateincluding the crystal layer of the group 13 nitride

Here, the method of separating the crystal layer of the group 13 nitridefrom the single crystal substrate is not limited. According to apreferred embodiment, the crystal layer of the group 13 nitride isnaturally separated from the single crystal substrate, during a coolingstep after growing the crystal layer of the group 13 nitride.

Alternatively, the crystal layer of the group 13 nitride may beseparated from the single crystal substrate by chemical etching.

Etchants for performing the chemical etching may preferably be a strongacid such as sulfuric acid, chloric acid or the like, mixed solution ofsulfuric acid and phosphoric acid, or a strong alkali such as sodiumhydroxide aqueous solution, potassium hydroxide aqueous solution or thelike. Further, the chemical etching may preferably be performed at atemperature of 70° C. or more.

Alternatively, the crystal layer of the group 13 nitride may be peeledoff from the single crystal substrate by laser lift-off method.

Alternatively, the crystal layer of the group 13 nitride may be peeledoff from the single crystal substrate by grinding. Alternatively, thecrystal layer of the group 13 nitride may be peeled off from the singlecrystal substrate with a wire saw.

(Free-Standing Substrate)

The crystal layer of the group 13 nitride may be separated from thesingle crystal substrate to obtain a free-standing substrate.

The term “free-standing substrate” as used in the present inventionmeans a substrate that cannot be deformed or broken under its own weightduring handling and can be handled as a solid. The free-standingsubstrate of the present invention can be used not only as a substratefor various types of semiconductor devices such as light emittingdevices, but also as a member or a layer other than the base material,such as an electrode (which may be a p-type electrode or an n-typeelectrode), a p-type layer, or an n-type layer. The free-standingsubstrate may include one or more of the other layers.

In the case that the crystal layer of the group 13 nitride forms thefree-standing substrate, the free-standing substrate should have athickness that allows for free-standing and preferably has a thicknessof 20 μm or more, more preferably 100 μm or more, and further preferably300 μm or more. No upper limit should be set on the thickness of thefree-standing substrate, but it is realistic to have a thickness of 3000μm or less in terms of manufacturing cost.

(Method of Controlling Arithmetic Average Roughness Ra of Upper Surface)

It is not particularly limited the method of controlling the arithmeticaverage roughness Ra of the upper surface of the layer of the crystal ofthe group 13 nitride to 0.05 nm or more and 1.0 nm or less, and themethod includes grinding, polishing and etching, for example.

The polishing includes mechanical polishing by processing utilizing freeabrasives or chemical mechanical polishing (CMP) utilizing colloidalsilica or the like. The etching method includes reactive ion etching(RIE). The etching gas may preferably be a chlorine-based gas orfluorine-based gas.

(Composite Substrate)

It can be used the single crystal substrate with the crystal layer ofthe group 13 nitride provided thereon as a template substrate forforming another functional layer thereon without separating the crystallayer of the group 13 nitride.

(Functional Device)

It is not particularly limited a functional device structure provided onthe crystal layer of the group 13 nitride, it may have a function oflight-emitting function, rectifying function or electricpower-controlling function.

It is not limited the structure or production method of a light-emittingdevice using the crystal layer of the group 13 nitride of the presentinvention. Typically, the light-emitting device is produced by providinga light-emitting functional layer on the crystal layer of the group 13nitride. Further, the crystal layer of the group 13 nitride may be usedas an electrode (possible p-type electrode or n-type electrode), or amember or layer other than p-type layer or n-type layer or the like toproduce the light-emitting device.

FIG. 8 schematically shows the construction of layers according to anembodiment of the present invention. The light-emitting device 21 shownin FIG. 8 includes a free-standing substrate 13 and a light emittingfunction layer 18 formed on the substrate. The light-emitting functionlayer 18 provides light-emission based on the principle of alight-emitting device such as LED or the like by appropriately providingan electrode or the like and applying a voltage.

The light emitting functional layer 18 is formed on the substrate 13.The light emitting functional layer 18 may be provided entirely orpartially on the surface of the substrate 13 or may be provided entirelyor partially on a buffer layer to be described hereinafter if the bufferlayer is formed on the substrate 13. The light emitting functional layer18 may take one of various known layer configurations that provide lightemission based on the principle of light emitting devices as representedby LED's by appropriately providing electrodes and/or phosphors thereonand applying a voltage therebetween. Accordingly, the light emittingfunctional layer 18 may emit visible light of, for example, blue and redor may emit ultraviolet light without or with visible light. The lightemitting functional layer 18 preferably forms at least a part of a lightemitting device that exploits a p-n junction and the p-n junction mayinclude an active layer 18 b between a p-type layer 18 a and an n-typelayer 18 c, as shown in FIG. 8. In this case, a double heterojunction ora single heterojunction (hereinafter referred to collectively asheterojunction) may be employed in which the active layer has a bandgapsmaller than that of the p-type layer and/or the n-type layer. A quantumwell structure in which the active layer is thinned may also be taken asone form of p-type layer/active layer/n-type layer. A doubleheterojunction in which the active layer has a bandgap smaller than thatof the p-type layer and the n-type layer should obviously be employed toobtain a quantum well. Many quantum well structures may also be stackedto provide a multiple quantum well (MQW) structure. These structuresallow to have a higher luminous efficiency compared to p-n junction. Thelight emitting functional layer 18 thus preferably includes a p-njunction, a heterojunction, and/or a quantum well junction having alight emitting feature. Further, 20 and 22 represents examples ofelectrodes.

Accordingly, one or more layers forming the light emitting functionallayer 18 can include at least one or more selected from the groupconsisting of the n-type layer with n-type dopants doped therein, thep-type layer with p-type dopants doped therein, and the active layer. Inthe n-type layer, the p-type layer, and the active layer (if exists),the main components may be of the same material or may be ofrespectively different materials.

The material of each layer forming the light emitting functional layer18 is not particularly limited as long as grown in a manner generallyfollowing the crystal orientation of the crystal layer of the group 13nitride and having light emitting function, but preferably includes onetype or more selected from gallium nitride (GaN)-based material, zincoxide (ZnO)-based material, and aluminum nitride (AlN)-based material asthe main component and may appropriately contain dopants for controllingto be p-type or n-type. Gallium nitride (GaN)-based material isparticularly preferable. The material of the light emitting functionallayer 18 may be a mixed crystal with, for example, AlN, InN, etc.solid-solved in GaN to control the bandgap. As mentioned in the lastparagraph, the light emitting functional layer 18 may employ theheterojunction composed of multiple types of material systems. Forexample, the p-type layer may employ gallium nitride (GaN)-basedmaterial, while the n-type layer may employ zinc oxide (ZnO)-basedmaterial. Alternatively, the p-type layer may employ zinc oxide(ZnO)-based material, while the active layer and the n-type layer mayemploy gallium nitride (GaN)-based material, the combination ofmaterials being not particularly limited.

The film formation method for the light emitting functional layer 18 andthe buffer layer is preferably exemplified by a gas phase method such asMOCVD, MBE, HVPE, and sputtering, a liquid phase method such as Na fluxmethod, ammonothermal method, hydrothermal method, and sol-gel method, apowder method utilizing the solid phase growth of powder, and thecombinations thereof, though not particularly limited as long as beinggrown in a manner generally following the crystal orientation of thecrystal layer of the group 13 nitride.

EXAMPLES Inventive Example 1 (Production of Gallium NitrideFree-Standing Substrate)

An alumina film 2 with a thickness of 0.3 μm was film-formed bysputtering and a seed crystal film 3 composed of gallium nitride andwith a thickness of 2 μm was film-formed by MOCVD method on a sapphiresubstrate 1 with a diameter of 6 inches to provide a seed crystalsubstrate.

The seed crystal substrate was placed in an alumina crucible in a glovebox filled with nitrogen atmosphere. Then, gallium metal and sodiummetal were filled in the crucible so that Ga/Ga+Na (mol %) was made 15mol %, and the crucible was closed with an alumina plate. The cruciblewas contained in an inner container of stainless steel, which was thencontained in an outer container of stainless steel capable of includingit, and the outer container was then closed with a container lidequipped with a pipe for introducing nitrogen. The outer container waspositioned on a rotatable table provided in a heating part of a crystalproduction system which was subjected to baking under vacuum in advance,and a pressure-resistant container was sealed with a lid.

The inside space of the pressure-resistant container was then evacuatedby a vacuum pump to a pressure or 0.1 Pa or less. While an upper heater,middle heater and lower heater were adjusted to heat the heated insidespace to 870° C., nitrogen gas was introduced from a nitrogen gas bombeto 4.0 MPa, and the outer container was rotated around a central axis ata rate of 20 rpm clockwise and anti-clockwise at a predeterminedinterval. The acceleration time was made 12 seconds, holding time wasmade 600 seconds, deceleration time was made 12 seconds and stoppingtime was made 0.5 seconds. Such state was maintained for 40 hours.Thereafter, the temperature and pressure were lowered to roomtemperature and atmospheric pressure through natural cooling, the lid ofthe pressure-resistant container was opened and the crucible was takenout from the inside. Solidified sodium metal in the crucible was removedto collect a gallium nitride free-standing substrate without cracks andseparated from the seed crystal substrate.

(Evaluation)

The upper surface of the gallium nitride free-standing substrate waspolished and observed by CL by means of a scanning type electronmicroscope (SEM) with a CL detector. As a result, as shown in FIG. 3, itwas observed the high-luminance light-emitting parts emitting whitelight inside of the gallium nitride crystal by the CL photograph.Further, at the same time, as shown in FIG. 9, as the same visual fieldwas observed by SEM, voids were not confirmed and uniform galliumnitride crystal was proved to be grown.

Further, the gallium nitride free-standing substrate was cut along across section perpendicular to the upper surface, and the cut crosssection was polished and observed by CL by means of the scanning typeelectron microscope (SEM) with the CL detector. As a result, as shown inFIG. 6, it was observed the high-luminance light-emitting parts emittingwhite light inside of the gallium nitride crystal by the CL photograph.Further, at the same time, as shown in FIG. 7, as the same visual fieldwas observed by SEM, voids were not confirmed and uniform galliumnitride crystal was proved to be grown. That is, on the cross section ofthe crystal layer of the group 13 nitride, same as the upper surface,the high-luminance light-emitting parts were present according to the CLobservation, it was not present microstructure having the same orsimilar shape of the high-luminance light-emitting part shown in the CLphotograph, according to the SEM.

(Measurement of Dislocation Density)

It was measured the dislocation density of the upper surface of thecrystal layer of the group 13 nitride. The CL observation was performedto measure the density of dark spots at the dislocated positions so thatthe dislocation density was calculated. As a result of the observationof five visual fields each having sizes of 80 μm*105 μm, it was deviatedin a range of 1.2×10⁴/cm² to 9.4×10⁴/cm² with an average of 3.3×10⁴/cm².

(Measurement of Surface Tilt Angle)

It was measured the half value width at (0002) plane of X-ray rockingcurve on the upper surface of the crystal layer of gallium nitride,which was proved to be 73 seconds.

(Measurement of Surface Twist Angle)

It was measured the half value width at (1000) plane of X-ray rockingcurve on the upper surface of the crystal layer of gallium nitride,which was proved to be 85 seconds.

(Arithmetic Average Roughness Ra)

The arithmetic average roughness Ra of the upper surface of the thusobtained free-standing substrate was measured be means of an atomicforce microscope supplied by Hitachi High-Tech Science Corporation(Model: AFM5400L). It was used, as a cantilever, “MICRO CANTILEVEROMCL-AC160TS-C3” supplied by Olympus Corporation. It was applied, as themeasurement conditions, on dynamic focus mode at a scanning frequency of0.81 Hz and in a visual field of 10 μm×10 μm. It was used, as ananalytic software, “Nano Navi Real”. As a result, Ra was proved to be0.08 nm.

(Film Formation of Light-Emitting Function Layer by MOCVD Method)

Using MOCVD method, on the free-standing gallium nitride substrate, as an-type layer, it was deposited an an-GaN layer in 1 μm at 1050° C. dopedso that an atomic concentration of Si atoms became 5×10¹⁸/cm³. Then, asa light-emitting layer, it was deposited a multiple quantum well layersat 750° C. Specifically, five layers of well layers of 2.5 nm of InGaNand six layers of barrier layers of 10 nm of GaN were alternatelydeposited. Then, as a p-type layer, it was deposited a p-type GaN in 200nm at 950° C. doped so that an atomic concentration of Mg atoms became1×10¹⁹/cm³. Thereafter, it was taken out of an MOCVD apparatus and thensubjected to heat treatment at 800° C. in nitrogen atmosphere for 10minutes as an activating treatment of Mg ions in the p-type layer.

The pits were not observed on the surface of the thus obtainedlight-emitting functional layer.

(Production of Light-Emitting Device)

Using photolithography process and vapor deposition method, on theopposite side of the n-GaN layer and p-GaN layer of the free-standinggallium nitride substrate, Ti film, Al film, Ni film and Au film werepatterned in thicknesses of 15 nm, 70 nm, 12 nm and 60 nm, respectivelyas a cathode electrode. Thereafter, for assuring ohm contactcharacteristic, heat treatment was performed at 700° C. for 30 secondsunder nitrogen atmosphere. Further, using photolithography process andvapor deposition method, Ni film and Au film were patterned inthicknesses of 6 nm and 12 nm, respectively, as a transparent anode onthe p-type layer. Thereafter, for assuring the ohmic contactcharacteristic, heat treatment was performed at 500° C. for 30 secondsunder nitrogen atmosphere. Further, using photolithography process andvapor deposition method, on a partial region of a top surface of the Niand Al films as the transparent anode, Ni film and Au film werepatterned in thicknesses of 5 nm and 60 nm, respectively, as a pad forthe anode. The thus obtained substrate was cut into chips, which weremounted on lead frames to obtain light-emitting devices of vertical typestructure.

(Evaluation of Light-Emitting Device)

Hundred samples were arbitrarily selected from the thus produceddevices, and electricity was flown between the cathode and anode toperform the I-V measurement. Rectification was confirmed in 90 of thesamples. Further, current was flown in the forward direction to confirmthe luminescence of light of a wavelength of 460 nm.

(Adjustment of Arithmetic Average Roughness Ra of Upper Surface andFilm-Formation of Light-Emitting Layer)

The upper surface of the thus obtained free-standing substrate waspolished to control the arithmetic average roughness Ra at 0.05, 0.1 or1.0 nm. Further, Ra was adjusted as follows.

The upper surface with Ra of 0.05 nm was adjusted by performing CMP, theupper surface with Ra of 0.1 nm was adjusted by performing RIE, and theupper surface with Ra of 1.0 nm was adjusted by performing mechanicalpolishing.

The light-emitting functional layer was epitzxially grown by MOCVDmethod, as described above, on the upper surface of each of thefree-standing substrates. As a result, the surface pits were notobserved in all the cases.

(Production of a Device Having Rectifying Function)

A functional device having rectifying function was produced.

Specifically, a shot key barrier diode structure was formed on the uppersurface of the free-standing substrate obtained in the example, asfollows, and electrodes were then formed thereon to obtain a diode,followed by the confirmation of the characteristics.

(Film Formation of Rectifying Function Layer by MOCVD Method)

It was formed an n-GaN layer having a thickness of 5 μm, on thefree-standing substrate as an n-type layer using MOCVD method (organicmetal chemical vapor deposition) at 1050° C., so that it was doped withSi at an Si atom concentration of 1×10¹⁶/cm³.

Using photolithography process and vacuum deposition method, Ti/Al/Ni/Aufilms as an ohmic electrode were patterned on the surface on the sideopposite to the n-GaN layer of the free-standing substrate inthicknesses of 15 nm, 70 nm, 12 nm, and 60 nm, respectively. Thereafter,to improve ohmic contact characteristics, heat treatment at 700° C. wasperformed in nitrogen atmosphere for 30 seconds. Furthermore, usingphotolithography process and vacuum deposition method, Ni/Au films werepatterned as a shot key electrode on the n-GaN layer formed by MOCVDmethod in thicknesses of 6 nm and 80 nm, respectively. The substrateobtained in this way was cut into chips, which were mounted on leadframes to obtain the rectifying devices.

(Evaluation of Rectifying Device)

As a result of the I-V measurement, it was confirmed rectifyingproperty.

(Production of Electric Power-Controlling Device)

It was produced a functional device having the function of controllingelectric power.

It was produced a free-standing substrate as the example. However,different from the example 1, in producing the gallium nitride crystalby Na flux method, the doping of the impurity was not performed. On thesurface of the free-standing substrate obtained in this way, it wasproduced HEMT structure of Al_(0.25)Ga_(0.75)N/GaN by MOCVD method asfollows, an electrode is formed, and the transistor characteristics wereconfirmed.

Using MOCVD method (organic metal chemical vapor deposition), it wasformed an n-GaN layer without the doping of the impurity in a thicknessof 3 μm on the free-standing substrate as an i-type layer at 1050° C. Itwas then produced the Al_(0.25)Ga_(0.75)N layer as the functional layerin 25 nm at the same 1050° C. It was thus obtained the HEMT structure ofAl_(0.25)Ga_(0.75)N/GaN.

Using photolithography process and vacuum deposition method, Ti/Al/Ni/Aufilms as source and drain electrodes were patterned in thicknesses of 15nm, 70 nm, 12 nm, and 60 nm, respectively. Thereafter, to improve ohmiccontact characteristics, 700° C. heat treatment was performed innitrogen atmosphere for 30 seconds. Furthermore, using photolithographyprocess and vacuum deposition method, Ni/Au films were patterned as agate electrode by shot-key junction in thicknesses of 6 nm and 80 nm,respectively. The thus obtained substrate was cut into chips, which weremounted on lead frames to obtain the devices having the function ofcontrolling electric power.

(Evaluation of Electric Power-Controlling Device)

When the I-V measurement was performed, good pinch-off characteristicswere confirmed, in which the maximum drain current was 710 mA/mm andmaximum transconductance was 210 mS/mm.

Although the upper surface of the layer of the crystal of the group 13nitride was made N-plane in the examples, similar effects could beobtained in the case of Ga plane.

1. A layer of a crystal of a nitride of a group 13 element, said crystalof said nitride being selected from gallium nitride, aluminum nitride,indium nitride and the mixed crystals thereof and said layer comprisingan upper surface and a bottom surface: wherein said upper surfacecomprises a linear high-luminance light-emitting part and alow-luminance light-emitting region adjacent to said high-luminancelight-emitting part and said high-luminance light-emitting partcomprises a portion extending along an m-plane of said crystal of saidnitride of said group 13 element, said upper surface being observed bycathode luminescence; and wherein said upper surface has an arithmeticaverage roughness Ra of 0.05 nm or more and 1.0 nm or less.
 2. The layerof said crystal of said nitride of said group 13 element of claim 1,wherein said high-luminance light-emitting part substantially extendsalong said m-plane of said crystal of said nitride of said group 13element.
 3. The layer of said crystal of said nitride of said group 13element of claim 1, wherein a half value width of reflection at (0002)plane of an X-ray rocking curve on said upper surface is 3000 seconds orless and 20 seconds or more.
 4. The layer of said crystal of saidnitride of said group 13 element of claim 1, wherein voids are notobserved on a cross section substantially perpendicular to said uppersurface of said layer of said crystal of said nitride of said group 13element.
 5. The layer of said crystal of said nitride of said group 13element of claim 1, wherein a dislocation density on said upper surfaceof said layer of said crystal of said nitride of said group 13 elementis 1×10⁶/cm² or less.
 6. The layer of said crystal of said nitride ofsaid group 13 element of claim 5, wherein said dislocation density onsaid upper surface of said layer of said crystal of said nitride of saidgroup 13 element is 1×10²/cm² or more and 1×10⁶/cm² or less.
 7. Thelayer of said crystal of said nitride of said group 13 element of claim1, wherein said high-luminance light-emitting part forms a continuousphase; and wherein said low-luminance light-emitting region forms andiscontinuous phase divided by said high-luminance light-emitting part.8. The layer of said crystal of said nitride of said group 13 element ofclaim 1, wherein a half value width of reflection at (1000) plane of anX-ray rocking curve on said upper surface is 10000 seconds or less and20 seconds or more.
 9. The layer of said crystal of said nitride of saidgroup 13 element of claim 1, wherein said nitride of said group 13element comprises a gallium nitride series nitride.
 10. A free-standingsubstrate comprising said layer of said crystal of said nitride of saidgroup 13 element of claim
 1. 11. A functional device comprising: saidfree-standing substrate of claim 10; and a functional layer provided onsaid layer of said crystal of said nitride of said group 13 element. 12.The functional device of claim 11, wherein said functional layer has afunction of light-emitting function, rectifying function or electricpower-controlling function.
 13. A composite substrate comprising: asupporting body; and said layer of said crystal of said nitride of saidgroup 13 element of claim 1 provided on said supporting body.
 14. Afunctional device comprising: said composite substrate of claim 13; anda functional layer provided on said layer of said crystal of saidnitride of said group 13 element.
 15. The functional device of claim 14,wherein said functional layer has a function of light-emitting function,rectifying function or electric power-controlling function.